What's output data of a GPS receiver?

Question

What's output data of a GPS receiver? I have some information about NMEA but I want to know If all GPS receivers have same output or not?

thank you

Answer 1

More or less they have the same output. They differ only at very special topics, like raw data output option for special evaluations.

The GPS chip manufctures specify which NMEA sentences they support. You might want to read e.g the ublox protocoll specification downlodable from the ublox homepage.

The following NMEA sentences are widley used with GNSS modules;

GGA, GGL, GSA, GSV, RMC, VTG, ZDA

Note that the RMC sentence is the recommended minimum for navigation devices.

Answer 2

This highly depends on the receiver model used and what kind of data you are looking for. Basically, two different types of outputs can be available, position solutions (including velocities) or raw measurements (the observables for each satellite). Some receivers (the cheaper ones) are limited to position output, while other receivers can output the raw data as well. For positions, the NMEA format is quite handy, but not for raw measurements. These are usually output in a binary, proprietary protocol which is different between the various receiver manufacturers. However, most receivers include some tools which allow the transformation of these propietary protocols into the RINEX format. This is the "receiver independent exchange format", but is used for post-processing rather than for live output.

Additionally, professional GNSS receivers can be configured quite flexibly, so that the type of output, the update rate and the output port (network, serial ports, bluetooth, usb, ...) can be configured as desired.

A very handy toolkit to work with different types of GNSS receiver is the RTKLIB (http://www.rtklib.com/), an open-source program package for various tasks related to satellite navigation systems.